The removal of acid gases, e.g. hydrogen sulfide, carbonyl sulfide, and carbon dioxide, from industrial and natural gas streams is an important and frequently encountered operation in the process industry. It is known that in these processes, certain of the alkanol amines used react with carbon dioxide to form carbamate precursors. The formation of the carbamate precursors is detrimental to the scrubbing process since they can cause corrosion, have no acid gas removal properties and reduce solution capacity.
Historically, thermal reclaimers have been used to remove nonvolatile contaminants from the used scrubbing or wash solution. However, these thermal reclaimers pose difficulties in that high temperatures, long residence time, and dehydrating environment are typically encountered in such reclaimers. Moreover, there are many problems with conventional reclaimer designs and operations. In particular, in the high temperature dehydrating environment encountered in conventional thermal reclaimers, the carbamate precursors can be converted into amino ethers with permanent, concomitant loss of the alkanolamine. This presents a large problem since major loss of the alkanolamine translates into significant chemical replacement costs in the overall gas scrubbing operation. It is known that the production of these amine ethers in conventional recovery processes is accelerated by increased temperature and exposed residence times in the reclaimer.
Using diglycolamine (DGA) as an example, in the scrubbing operation, the DGA reacts with CO2 to form a carbamate precursor. The carbamate precursor can react with DGA to form N,N,bis(hydroxyethoxyethyl)urea (BHEEU). The BHEEU, at the high temperatures in a typical thermal reclaimer, can irreversibly degrade to morpholine, an amino ether, and DGA. Accordingly, there is a net loss of DGA from the system.
The equations below show the reaction sequence:

FIG. 3 is a graph taken from a paper entitled Saudi Arabian Experience with DGA Units and Related Sulfur Plants, by Lewis G. Harruff, Saudi Arabian Oil Co. It shows the relationship between morpholine make, temperature and residence time.